Moringa oleifera seeds as disinfectant in water treatment :optimization and modelling

Abstract

The high cost of water treatment and high cost of chemicals for disinfection makes it difficult to produce high quality drinking water particularly in the developing countries. The use of chlorine which causes disinfection by-products is a major concern especially in the developed countries. As a result of this, there is the need to look for a cheap alternative such as the use of plant material as substitutes for chemical disinfectant. Moringa oleifera is an extensively documented plant material used for the treatment of drinking water. Its seed extracts contain active agents having excellent coagulation properties and exerting in vitro bactericidal activity. However, lack of available literature on the statistical optimization using Response Surface Methodology and Artificial Neural Network, inactivation kinetics of the seed extract using different disinfection models and effect of different seed processing for the seed extracts are major aspect never been explored. This study aims to develop operation parameters for the seed extracts to be used as disinfectant for water treatment, which might be suitable for drinking purposes. The screening of different extraction methods on Moringa oleifera seed extracts processing against four bacterial strains was carried out. The optimization process, based on statistical experimental design, comprises of one-factor-at-a-time (OFAT), faced centred central composite design (FCCCD) under the response surface methodology (RSM) and artificial neural network (ANN) using MATLAB 2012A were used to identify and determine the optimum process conditions. The multivariate regression analysis of the disinfection kinetic models was analysed using SPSS version 20 and the final application of the optimized process conditions with river water was evaluated. The results, based on qualitative and quantitative analysis, reveal that defatted seed cake with salt extraction was the best extraction method that inhibited bacterial strains with MBC/MIC ratio of 2 on Escherichia coli and Pseudomonas aeruginosa strains indicating that the seed extract exhibits strong bactericidal action. The statistical analysis of optimization results using RSM complemented with ANN gave a high coefficient of determination (R2) of 0.9992 and 0.9886 for P. aeruginosa and E. coli respectively. The model developed was verified and the optimum process parameters were 124 mg/l dosage, 65 minutes of contact time, 110 rpm mixing rate for E. coli bacterial strain and 125 mg/l dosage, 60 minutes of contact time and 130 rpm mixing rate for P. aeruginosa strain. The order of reaction followed second order and the inactivation kinetics showed that modified Hom model best fits the disinfection process with R2 of 0.9990. The findings from the application of the seed extract to river water shows that the seed extract can be used as a coagulant and disinfectant. The removal efficiency for the seed extract shows reductions in water parameters with over 99.98% reduction of total coliforms and heterotrophic bacteria after the disinfection process. The final treated water was benchmarked with the Malaysian drinking water standard and almost all of the water parameters were below the maximum acceptable range except for the total coliform. Hence, the findings of this study showed that defatted Moringa oleifera seed extract using the salt extraction method can be used as a disinfectant. This extract is recommended to be used in small communities in developing countries and in emergency situations. The mode of attack of the seed extract is recommended for further studies.